Hello, I was surprised about really big differences in running times between 6.4 and 6.4.1, whereby 6.4.1 is *much* slower: *** 6.4: cpu-time interesting (3,3): 00:01:38.08 *** 6.4.1: cpu-time interesting (3,3): 00:05:58.91 Here we have a factor of about 3.6!! Are there others that have noticed such behavior? What could be the reason for that? Sorry, my example is a small monster, but at the moment there is neither time left to search for the reason for this behavior nor to break it down to some smaller pieces of code. I just noticed it... However, you can find the source tree in http://liinwww.ira.uka.de/~rahn/src/ The file http://liinwww.ira.uka.de/~rahn/src/prog.tar.gz contains the tree as well. For the output above: Extract, cd proj/prog and run rahn@i90pc18:~/local/proj/prog$ for version in 6.4 6.4.1; do find . -name '*.hi' | rm -f ; ghc-$version --make -Wall -cpp -D__POS__='__FILE__ ++ "[" ++ show(__LINE__::Int) ++ "]: " ++ ' -fglasgow-exts -fallow-overlapping-instances -fallow-undecidable-instances -O Prog/Interesting.hs -o Prog/Interesting.$version.bin 2>/dev/null >/dev/null; echo -n "*** $version: " ; ./Prog/Interesting.$version.bin 2>&1 | grep time ; done Regards, Mirko P.S.: I run a debian-box with i686 GNU/Linux 2.6.11.11 and a dualcore P4 3.2 GHz. -- -- Mirko Rahn -- Tel +49-721 608 7504 -- --- http://liinwww.ira.uka.de/~rahn/ ---